Hydraulic braking systems for vehicles

ABSTRACT

In an hydraulic braking system for vehicles a pedal-operated booster-assisted hydraulic master cylinder assembly ( 1 ) is adapted to apply a vehicle brake ( 2 ) by the supply of hydraulic fluid under pressure to a brake actuator for operating the brake, and a proportional valve ( 50 ) is arranged to provide a quick-fill function for the brake actuator in response to a proportional pilot signal ( 40 ) from the master cylinder assembly.

BACKGROUND OF THE INVENTION

This invention relates to hydraulic braking systems for vehicles of thekind in which a pedal-operated booster-assisted hydraulic mastercylinder assembly is adapted to apply a vehicle brake by the supply ofhydraulic fluid under pressure to a brake actuator for operating thebrake.

In braking systems, particularly for vehicles of the “off-highway type”,such as tractors and earth moving equipment, the trend is to adopt largerunning clearances between the braking members of the brake, for examplebetween friction members and rotatable discs, in order that frictionloses arising from parasitic drag are reduced or substantiallyeliminated.

We are aware of GB-A-2179715 which forms the pre-characterising portionof claims 1 and 8.

SUMMARY OF THE INVENTION

According to our invention in an hydraulic braking system of the kindset forth for vehicles, a proportional valve is arranged to provide aquick-fill function for a wheel brake actuator in response to aproportional pilot signal from the master cylinder assembly, and thebooster includes first and second pistons which are relatively moveableto close a port leading to a reservoir and to open a proportionalpressure port through which the pilot signal comprising hydraulicpressure generated in the space between the pistons by relative movementtherebetween is directed to and opens the proportional valve.

The quick-fill function compensates for additional fluid volumerequirements, and ensures that the pedal is immediately responsive withsuch additional volume requirements.

The proportional valve may be situated in any convenient location, forexample in close proximity to the brake actuator.

In one construction, in a normal operative mode, the booster is adaptedto meter input pressure to provide a booster signal, with the meteredside of the booster being connected into and at a pressure,substantially equal to the pilot signal of the proportional valve.

As the pilot signal is applied to the proportional valve, theproportional valve will open, allowing hydraulic fluid to flow fromavailable vehicle hydraulics into the brake actuator.

The “quick-fill” function works until a pre-set pressure is reached,directly proportional to the pilot signal provided by the booster whichis also directly proportional to the effort applied by the pedal.

Preferably the setting of the proportional valve is such that allclearances are taken up by utilising available vehicle hydraulics andthereafter the proportional valve is adapted to close allowing allfurther braking to be applied directly from the master cylinder.

The invention allows rationalisation of boosters into fewer sizes tomeet customer requirements. By tuning the proportional valve orpre-setting the setting of the proportional valve, the clearances of thebrake may be taken up accordingly, and higher pressure brake stiffnessesmay be applied through one size of master cylinder for all applications.

The invention is particularly applicable to a dual braking system inwhich brakes on wheels on opposite sides of the vehicle may be operatedsimultaneously for braking, or independently to assist steering. Whenoperated simultaneously pressure spaces in the two master cylinderassemblies are interconnected to compensate for differential wear oflinings of the brakes.

BRIEF DESCRIPTION OF THE DRAWINGS

One embodiment of our invention is illustrated in the accompany drawingsin which:

FIG.1 is a layout of a dual hydraulic braking system for “off-highway”vehicles;

FIG. 2 is an exploded view of a proportional pressure port incorporatedin each of a pair of pedal-operated booster hydraulic master cylinderassemblies; and

FIG. 3 is a layout similar to FIG. 1 but showing a modification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the braking system illustrated in the layout of FIGS. 1 and 2, apedal-operated booster assisted hydraulic master cylinder assembly 1 isadapted to operate a brake actuator 2 in order to apply a brake on theright-hand side of a vehicle, and a similar pedal-operated boosterassisted master-cylinder assembly 3 is adapted to operate a brakeactuator 4 in order to apply a brake on a wheel on the opposite side ofthe vehicle. The two master cylinder assemblies are identical so thatonly the assembly 1 will be described in detail.

The pedal-operated booster assisted hydraulic master cylinder assembly 1comprises a housing 5 having a stepped longitudinal bore 6 which isclosed at its inner end and which comprises an outer bore portion 7 ofgreater diameter and an inner bore portion 8 of smaller diameter. Afirst stepped piston 9 works in the bore 6. A closure member 10 of“top-hat” section closes the outer end of the bore portion 7 and isdisposed between the piston 9 and a stop defined by a mounting bracket11. An internal bore 12 in the piston 9 and an internal bore 13 in theclosure member 10, and which is of smaller diameter than the bore 12together constitute a stepped bore in which works a second steppedpiston 14 upon which a brake pedal 15 acts through an operating rod.Normally the piston 14 is held in a retracted position in which ashoulder at the step in diameter co-operates with the closure member 10in turn to hold it in engagement with the stop 11 as biased by theloading in an internal return spring 16. Similarly a compression spring17 acts on the piston 9 to hold it in a retracted position in engagementwith the piston 13, the spring 17 being stronger than the spring 16. Athird compression return spring 18 housed in a pressure space 19 definedby the bore portion 8 which is of smaller diameter also acts on thepiston 9. The pressure space 19 is connected to the brake 2 through apipe line 20.

The system is provided with a source 30 of high pressure fluidcomprising a pump 31 driven by a motor 32 and which is adapted to drawhydraulic fluid from a reservoir 33 to charge an hydraulic accumulator34 through a one-way valve 35. An outlet from the supply 30 is connectedthrough a pipeline 36 to the master cylinder 1 through an inlet port andwhich, in the off position shown in the drawings, is isolated from apressure space 38, in which the spring 16 is located, by a seal 39carried by the piston 9.

A proportional pressure port 40 in the wall of the housing 5 is normallyclosed by a seal 41, also carried by the piston 9, and an annularchamber 42 defined between the bore 6 and two seals 39 and 41communicates with a space between the pistons 14 and the bore 12 througha radial port 45. In the retracted position shown in the drawings freecommunication is allowed through the port 45 and past a seal 46 carriedby the piston 14.

The proportional port 40 is connected to a proportional valve 50 througha pipe-line 51 and the proportional valve 50 is located in closeproximity to the brake actuator 2. Normally the proportional valve 50 isclosed to isolate the brake actuator 2 from vehicle hydraulics 52.

In the retracted, inoperative, position illustrated in the drawings thecomponents of the master cylinders 1,3 are at rest with all the chambersof the master cylinders connected to respective reservoirs 60 and 61 ofhydraulic fluid and which, in turn, are connected to their respectivepressure spaces 19 through recuperation ports 62, and to theproportional valves 50 through the respective ports 45. The highpressure source 30 is isolated from the master cylinders 1,3 by closureof inlet ports, and the proportional pressure ports 40 are also closed.

When a master cylinder, say the master cylinder 1, is operated by thepedal the stepped pistons 14 and 9 are advanced so that fluid underpressure enters the space 42 and into the proportional pressure port 40,in turn to pressurise the pressure space 38. The piston 9 is thenadvanced to pressurise fluid in the pressure space 19 which, in turn, issupplied to the brake actuator 2. During this movement of the pistons 9,14 relative movement between them also takes place, the proportionalpressure port 40 is opened, and the port 45 is closed by the seal 46. Aproportional pilot signal comprising hydraulic pressure in the spacebetween the pistons 9 and 14 is therefore directed to the respectiveproportional valve 50 which then opens to allow hydraulic fluid to“quick-fill” into the brake actuator 2.

The “quick-fill” aspect works until a pre-set pressure is reached,directly proportional to the pilot signal provided by the mastercylinder 1 and which is also directly proportional the effort providedby the pedal 15.

The setting of the proportional valve 50 is also such that allclearances are taken up utilising the available vehicle hydraulics.Thereafter the proportional valve closes allowing further braking to beapplied directly from pressurised fluid supplied to the brake actuator 2from the pressure space 19.

The pre-set pressure is tailored to the requirements of the vehiclebraking system.

When braking is no longer required the pedal is released and returns tothe position illustrated in the drawings, and hydraulic fluid isreturned to the reservoir 60 through the recuperation port 62 in thewall of the housing 5.

Since the construction and the operation of the master cylinder 3 issimilar to that of the master cylinder assembly 1 any furtherdescription is considered unnecessary.

When both master cylinder assemblies 1 and 3 are operated simultaneouslyto apply brakes on opposite side of the vehicle, respective pressurespaces 19 are interconnected by a valve controlled compensating passage70 which is in open communication when both pedals are operatedtogether. This compensates for differential wear of the linings of thetwo brakes.

In the braking system illustrated in the layout of FIG. 3 of theaccompanying drawings the source 30 is omitted, and the volume ofhydraulic fluid from the vehicle hydraulics 65 is utilised to providethe quick-fill function described above.

The construction and operation of the system illustrated in the layoutof FIG. 3 is otherwise the same as that of FIG. 1 and correspondingreference numerals have been applied to corresponding parts.

The foregoing description is only exemplary of the principles of theinvention. Many modifications and variations of the present inventionare possible in light of the above teachings. The preferred embodimentsof this invention have been disclosed, however, so that one of ordinaryskill in the art would recognize that certain modifications would comewithin the scope of this invention. It is, therefore, to be understoodthat within the scope of the appended claims, the invention may bepracticed otherwise than as specially described. For that reason thefollowing claims should be studied to determine the true scope andcontent of this invention.

What is claimed is:
 1. A hydraulic braking system for a vehicle having ahydraulic master cylinder assembly adapted to apply a vehicle brake bysupplying hydraulic fluid under pressure to a brake actuator, the systemcomprising: a proportional valve operatively coupled to the brakeactuator; and a booster operatively coupled to the proportional valve,the booster having a port leading to a hydraulic fluid reservoir, afirst piston and a second piston, said first and second pistons beingrelatively movable to close the port, and a proportional pressure portthrough which a proportional pilot signal from the master cylinderassembly is directed, wherein the proportional pilot signal correspondsto hydraulic pressure generated in a space between said first and secondpistons by relative movement therebetween, and wherein said proportionalpressure port opens from the relative movement of the first piston andthe second piston to open said proportional valve in response to theproportional pilot signal to allow the hydraulic fluid to quick fillinto the brake actuator.
 2. The braking system as recited in claim 1wherein said booster meters input pressure to provide a booster signal,with a metered side of said booster being connected into and at apressure substantially equal to the hydraulic pressure corresponding tothe proportional pilot signal of said proportional valve so that as theproportional pilot signal is applied to said proportional valve, saidproportional valve opens to allow hydraulic fluid to flow into saidbrake actuator.
 3. The braking system as recited in claim 1 wherein thequick-fill function operates until a pre-set pressure is reached,wherein the pre-set pressure is directly proportional to theproportional pilot signal.
 4. The braking system as recited in claim 1,wherein a setting of said proportional valve is such that brakingclearances between said first and second pistons are taken up byutilizing available hydraulic fluid and thereafter said proportionalvalve is adapted to close, allowing all further braking to be applieddirectly from said master cylinder assembly.
 5. A dual hydraulic brakingsystem comprising: a first and a second hydraulic master cylinderassembly, each master cylinder assembly including a pressure space forconnection to a brake; a valve controlled compensating passageinterconnecting pressure spaces in the first and the second mastercylinder assembly; a first proportional valve operatively coupled to afirst wheel brake actuator associated with the first master cylinderassembly and a second proportional valve operatively coupled to a secondwheel brake actuator associated with the second master cylinderassembly; and a first booster operatively coupled to the firstproportional valve and a second booster operatively coupled to thesecond proportional valve, the first and second boosters each having aport leading to a hydraulic fluid reservoir, a first piston and a secondpiston, said first and second pistons being relatively movable to closethe port, and a proportional pressure port through which a proportionalpilot signal from one of the first and second master cylinder assembliesis directed, wherein the proportional pilot signal corresponds tohydraulic pressure in a space between said first and second pistons, andwherein said proportional pressure port opens from relative movement ofthe first piston and the second piston to open one of said first andsecond proportional valves in response to the proportional pilot signalto allow the hydraulic fluid to quick fill into one of the first andsecond wheel brake actuators.
 6. The braking system as recited in claim5 wherein one of said first and second booster meters input pressure toprovide a booster signal, with a metered side of said booster beingconnected into and at a pressure substantially equal to the hydraulicpressure corresponding to the proportional pilot signal of one of saidfirst and second proportional valves so that as the proportional pilotsignal is applied to one of first and second said proportional valves,said one of said first and second proportional valves opening to allowhydraulic fluid to flow into one of said first and second brakeactuators.
 7. The braking system as recited in claim 5 wherein thequick-fill function operates until a pre-set pressure is reached,wherein the pre-set pressure is directly proportional to theproportional pilot signal.
 8. The braking system as recited in claim 5,wherein a setting of one of first and second said proportional valves issuch that braking clearances between said first and second pistons aretaken up by utilizing available hydraulic fluid and thereafter said oneof said first and second proportional valves is adapted to close,allowing all further braking to be applied directly from said mastercylinder assembly.